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A closed loop AGC circuit for a digital side of a dual mode cellular telephone wherein receiver and transmitter adjustable amplifiers are controlled by a linear feedback control system including a linear signal level detector which determines signal levels after a receiver baseband demodulator stage

A closed loop AGC circuit for a digital side of a dual mode cellular telephone wherein receiver and transmitter adjustable amplifiers are controlled by a linear feedback control system including a linear signal level detector which determines signal levels after a receiver baseband demodulator stage. The linear signal level detector receives a signal at an AC signal level and produces, through an averaging process, a DC received signal strength indication at a DC signal level which is linearly proportional to the AC signal level. The received signal strength indication is compared to a reference signal to produce a gain control signal which is linearly inverted and supplied as a receive gain control signal to the receiver adjustable amplifiers. The gain control signal is also combined with a transmit adjust signal received from the base station and supplied as a transmit gain control signal to the transmitter adjustable amplifiers.

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A code division multiple access (CDMA) automatic gain control circuit for a CDMA cellular telephone, said circuit comprising: a CDMA adjustable receiver amplifier including a gain control input, a signal input, and a signal output; a CDMA adjustable transmitter amplifier including a gain control inp

A code division multiple access (CDMA) automatic gain control circuit for a CDMA cellular telephone, said circuit comprising: a CDMA adjustable receiver amplifier including a gain control input, a signal input, and a signal output; a CDMA adjustable transmitter amplifier including a gain control input, a signal input, and a signal output; and a CDMA linear feedback control system including a linear, non-logarithmic signal level detector including an input and an output, wherein said input of said linear, non-logarithmic signal level detector is coupled to said signal output of said CDMA adjustable receiver amplifier, wherein said linear, non-logarithmic signal level detector includes means for, upon receiving an input signal with an alternating current (AC) component and a direct current (DC) component, blocking the DC component of the input signal to leave only the AC component of the input signal, means connected to said blocking means for adding to said input signal a second DC component linearly proportionate to said AC component to produce a shifted signal having the second DC component and an AC component similar to the AC component of the input signal, and means connected to said adding means for receiving said shifted signal and for removing said AC component of the shifted signal to produce a detector output signal including substantially only the second DC component; and a comparator including a detection input, a reference input for receiving a reference signal, and an output, wherein said detection input of said comparator is coupled to said output of said linear signal level detector, and wherein said output of said comparator is coupled to said gain control input of said CDMA adjustable receiver amplifier and said gain control input of said CDMA adjustable transmitter amplifier.